This invention is in the field of semiconductor integrated circuits, and is more specifically directed to voltage regulators implemented in a large scale integrated circuit.
Many modern electronic devices and systems, particularly those performing control and other analog functions, rely upon the generation and use of a stable regulated voltage. For example, integrated circuits for controlling motors, such as disk drive controllers in a desktop or laptop computer system or workstation, require a regulated voltage to supply the voltages required by the digital circuits operating in the disk drive. A stable regulated voltage is required to ensure that the operation of the digital circuits remains stable and consistent over varying temperature conditions, load conditions, power supply voltage levels (particularly in battery-powered systems such as laptop computers), and the like.
Several voltage regulator circuit techniques are well known in the art. A simple type of regulator is the so-called “linear” voltage regulator. As is fundamental in the art, the linear regulator includes a pass device which selectively connects an input voltage to the regulator output, at which a circuit load is connected. Control circuitry senses the output voltage, compares it to a desired regulated output voltage level, and controls the pass device according to the comparison, so that the output voltage is maintained at the desired level. Linear regulators are quite simple and inexpensive to implement using conventional integrated circuit technology.
However, linear voltage regulators are somewhat limited in their performance. Linear regulators can only regulate a voltage below the input voltage; indeed, a specified parameter of typical linear regulators is the “drop-out” voltage, which is the difference between the input voltage and the maximum output voltage that can be regulated. Even modern LDO (“low drop-out”) regulators involve a drop-out voltage of on the order of a diode voltage drop.
Another type of voltage regulator is the “switching” regulator. The switching regulator involves an inductor at its output, and is based on the fundamental premise that, while the current through an inductor cannot change instantaneously, the voltage across the inductor can change instantaneously. In general, switching regulators involve a switching device, or pass device, that selectably switches the input voltage source into and out of an inductor. Typically, a pulse-width modulated signal controls the switching device, so that the output voltage is a function of the amplitude of the input voltage and the duty cycle of the switching device. Variations in the configuration of the switching regulator are possible, and achieve a great deal of design flexibility. Switching regulators of the “Buck” type regulate an output voltage that is lower than the input voltage, and switching regulators of the “Boost” type can generate an output voltage that is regulated above the voltage of the input. Other variations of switching regulators generate a regulated voltage that is of a negative polarity relative to the input voltage (e.g., in “Buck-Boost” inverting regulators), or generate multiple regulated output voltages (e.g., in “Flyback” switching regulators). Switching regulators are also often referred to as voltage “converters”. In any of these forms, switching regulators typically provide higher power conversion efficiency.
However, switching regulators are typically more costly to implement than are linear regulators. The circuitry for controlling the switching operation is typically more complex than in the linear regulator, and involves additional devices and intelligence. In addition, the switching regulator involves the use of an inductor in the circuit. As well known in the art, significant inductance cannot be readily realized in a solid-state integrated circuit, thus requiring an external component to be connected to effect the switching regulator function.
The charge pump voltage regulator is also well known in the art. Typical charge pump circuits involve a capacitor that is periodically charged through a diode, again to attain a voltage that depends on the input voltage amplitude and the duty cycle of the switched charging. The diode permits the voltage at the capacitor to exceed that of the input voltage, or to be charged to a voltage that is of the opposite polarity of the input voltage. Charge pumps have been used, for example, to generate a negative substrate voltage that sets the back-gate bias of metal-oxide-semiconductor (MOS) transistors in the integrated circuit, thus controlling device performance. Charge pumps may also be used in place of switching regulators, especially in those circuits and devices in which an inductor is not available or is undesirable.
As evident from this discussion, the selection of an appropriate voltage regulator depends upon several factors including the desired output voltage, the performance of the regulator, and also whether external components such as inductors may be utilized or are desired. Because this tradeoff involves the ultimate end equipment design, the manufacturer of integrated circuits including voltage regulators may be required to produce similar integrated circuits that embody different voltage regulator schemes. In addition, it has been observed that some end equipment manufacturers may utilize the same integrated circuit in multiple implementations, in which different voltage regulator types may be useful. In this situation, the end equipment manufacturer is faced with either maintaining inventory of separate integrated circuits for the separate implementations, or with using a less-than-optimal voltage regulator in some system implementations.
It is known to construct integrated circuits that include multiple voltage regulator topologies. FIG. 1 is an example of such a conventional integrated circuit 10. In this example, integrated circuit 10 includes functional circuitry 12, which is the appropriate logic circuitry, analog circuitry, memory circuitry, or the like that carries out the overall function of integrated circuit 10. In this conventional integrated circuit 10, voltage regulators 18a, 18b are provided, where voltage regulator 18a is of one type and voltage regulator 18b is of another type. In this conventional arrangement, each of voltage regulators 18a, 18b have dedicated external terminals from integrated circuit 10, as illustrated in FIG. 1. These dedicated terminals output the regulated voltage to other integrated circuits, and are also provided so that the appropriate external components (e.g., an inductor for a switching regulator) may be connected to the corresponding voltage regulators.
Conventional dual voltage regulator integrated circuits (i.e., lacking other functional circuitry 12 as in the case of FIG. 1) are also known. An example of which is the ON SEMICONDUCTOR CS5111 device, available from Semiconductor Components Industries, LLC. The CS5111 device, for example, includes a switching regulator and a linear regulator, and serves as a regulated power supply for electronic devices and systems. In this device, the switching regulator and linear regulator are substantially separately implemented, and have separate dedicated terminals, along the lines of that shown in FIG. 1.
It has been observed, in connection with this invention, that the implementation of separate multiple voltage regulators, as carried out in conventional integrated circuits is quite inefficient. Certain elements within conventional voltage regulators can occupy significant chip area. For example, feedback capacitors for error amplifiers within the sense and control loop of conventional voltage regulators can be quite large. The implementation of two separate voltage regulators according to conventional techniques is therefore costly in terms of chip area. In integrated circuits having significant functional circuitry, a large number of terminals (inputs, outputs, and common input/output terminals) are often required. In these large scale integrated circuits, the provision of each external terminal can be quite costly, not only in package size and complexity, but also in the chip area required to safely route signals to the external terminal. It is therefore desirable to minimize the number of external terminals for large scale integrated circuits.